Psalm 93 appears three times in the liturgy: as the Psalm of the Day for Friday, at the conclusion of Kabbalat Shabbat prior to Ma'ariv, and in P'sukei d'Zimra of Shabbat/Festival mornings. It is also briefly quoted in the Malchuyot section of the Rosh Hashana musaf amida. The Talmud in Masechet Rosh Hashana states that this psalm describes God's completion of the creation (i.e. on the 6th day), and it is for this reason it was chosen as the daily psalm. Some have suggested that the imagery of rivers and seas hint at a polemic against ancient Near Eastern creation myths. One of the essential modes of Ashkenazi chazzanut is known as "Adonai Malach". It is similar to the Western mixolydian mode (a major scale with a flattened 7th), and is used for many parts of the liturgy, including the beginning of the Amida repetition on Shabbat/Festivals, and for Kabbalat Shabbat as a whole. There is a tremendous irony to this identification, as the mode is so named for the inclusion of this psalm in Kabbalat Shabbat, yet in today's service, the mode changes to minor (aka Magen Avot) at Mizmor Shir, remaining so until the kaddish at the end of the service, and therefore Adonai Malach is not said using the Adonai Malach mode! This was obviously not the case historically in the Ashkenaz service, and in Nusach S'fard today, the Adonai Malach mode persists until after the Amida (where it appropriately changes to the eponymous Magen Avot for that prayer). Samuel Alman's enigmatic composition for Psalm 93 is the third and most singable of his settings. Whilst this melody used to be more widely known in London, today it is more of a curio. Alman alternates back and forth between Adonai Malach and Mi Sheberach tonalities, before breaking out into major at "Eidotecha" and concluding the final line in Magen Avot, which is perhaps a wonderful metaphor for the confusion of modes in which we find ourselves for the contemporary Shabbat evening service.